Electrical measuring instrument.



No. 698,647. Patented Apr. 29 I902.

T. DUNCAN.

ELECTRICAL MEASURING INSTRUMENT.

(Application filed A151. 22, 1899.)

(No Model.) 3 Sheets-Sheet l.

q/vi/tweoow v M Z24 Mom No.-69.8,647. Patented Apr. 29, I902. T. DUNCAN.

ELECTRICAL MEASURING INSTBUMENI.

[Appligstion filed Apr. 22, 1899.)

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(No Model.)

vwmboz M1110" wunmeron, u. c.

No. 698,647. Patented Apr. 29, I902.

T. DUNCAN.

ELECTRICAL MEASURING INSTRUMENT.

(Application filed Apr. 22, 1899.)

(No Model.) A N 3 Shee '(s-Shaet 3.

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wi/bvwoow Z 5W0? M 35 Mau UNITED STATES P TENT OFFICE.

THOMAS DUNCAN, OF OAKPARK, ILLINOIS, ASSlGNOR TO THE SIEMENS d HALSKEELECTRIC COMPANY OF CORPORATION OF ILLINOIS.

AMERICA, on CHICAGO, ILLINOIS, A

ELEC TRICALM EASU RING INSTRUMENT.

srnorrica'rioiv forming part of Letters Patent No. 698,647, dated April29, 1902.

Application filed Apri1'22, 1899.

To all wito'ml it may concern;

Be it known that I, THOMAS DUNCAN, of

Oakpark, in the county of Cook-and State of Illinois, have inventedcertain new and use- 5 fullmprovementsin Electrical Measuringlnstruments, of which the following is a specification. r

This invention relates to improvements in indicating instruments-such asammeters, voltmeters, wattmeters, and the likefor measuring electriccurrents; and it has for its object to provide an improved constructionin instruments of this character by which a more evenly distributed andincreased armature torque issecured without additional expenditure ofenergy and in which the armature acts both as aniotor part and as a dragtending to dampen or check its own. movement, and thereby to render theinstrument more nearly dead-beat in its action.

In the accompanying drawings, illustrating some of the forms in whichthe invention may be practically embodied, Figure 1 is a front elevationof a volt or am meter constructed in accordance with my invention. Fig.2 is a somewhat diagramm'atic view of another form of voltmeterconstruction. Fig. 3 is a similar view of a wattmeter construction. Fig.4: is a detail elevation of one form of improved armature-cylinderremoved from the instrument. Fig. 5 is an axialfsection thereof. Figs.6, 7, and. 8 are end views, showing different ways in which the coilsmay be wound on the armature in accordance with my invention. Fig. 9isanaxial section of another form of armature-cylinder. Fig. 10 shows thedetails of the armaturemounting in the instrument illustrated in Fig. 1.

The general construction of one form of indicating instrument to whichmy improvements are applicable is shown-in Figs. 1 to 10. Adesignates anarmature that is mounted to rotate between magnetic fields B, and themovements of which armature areindicated by'a pointer C upon aconveniently-located scale D, the torque of thearmature as energizedby'thepassing current being exerted against the tension of springsE,whioh are so applied that the amount of armature Serial No. 714,018.(No model.)

movement, as indicated by the pointer on thescale, is alwaysproportional to the current strength, pressure, or energy, as the casemay be, of the circuit in which the instrument is connected. As hereinshown, the armatureA is rigidly mounted upon a shaft a, which rotatesbetween pivot-bearings 1), carried by supporting-spiders B, that are inthis instance conveniently secured by screws 1) to the field-magnets B.The pointer C is rigidly attached to the shaft A, and the springs E areshown as applied between said shaft and the spiders l3, adjustment ofthe tension of the springs being provided for by securing the outerextremity e ofeachspring "to an inwardly projecting lug or finger 11These details of the armature-mounting have, however, nothing to' dowith thepresent improvements, which particularly concern theconstructing and winding of-the armature ,itself. This consists, asherein shown, of a cylinder, of aluminium, copper, or like non-magneticmetal, upon which the armature-coils A are. wound. These coils are shownas three or more in number and are distributed over the surface of thecylinder A, so as to produce as even a torque as possible in allpositions of the armature movement. This method of winding also enablesthe coils to be made verythin, as by but a single layer or soof wire, asshown,- so that it is possible to bring the magnetic fields B very closeto the armature, and thereby to gain in, efiective torque in proportionsto the decreased air-gap. A fourth and important advantage of thisconstruction of the armature lies in the fact that the varying magneticflux passing through the walls of the armature as the current varies inthe connected circuit .sets up eddy-currents in the latter tending toresist its motion and bring it to rest. The armature thus actsautomatically as a drag upon its own movement, and thezpointer tends tocome to rest immediately after responding to the current changes, sothat the instrument is rendered dead-beat in its action. This retardingeffectmay be increased by insertingsome magnetic material in thearmature to drawthe magnetic flux through more strongly. Thus in theconstruction shown in Figs. 4 and 5 a number of disks A are mountedtransversely within the cylinder for this purpose, While in Fig. 9 thecylindric armatureA is shown as provided with an iron lining A to thesame end.

In the voltmeter construction shown diagrammatically in Fig. 2 themagnetic fields B are coils, which are connected in series with thearmature-coils A in the shuntFcircuit. In the wattmeter shown in Fig.8these coils are connected in series in the circuit.

Figs. 6, 7, and 8 show some of the various ways in which the windingscan be distributed on the armature, and it will be understood that agreat variety of changes may be made in this feature and in the shape ofthe armature and other details without involving any departure from theinvention claimed.

For alternating-current work an armature, of rubber or othernon-metallic material, may be used, but obviously without the damping orretarding effect before referred to.

I claim as my invention- 1. An indicating electric meter provided withan armature comprising an outer shell of non-magnetic metal, and aninner lining of magnetic metal, and coils mounted on said armature andconnected in the circuit to be measured.

2. In an electric meter,the combination with an armature-winding, of anouter-shell of nonmagnetic metal fixed with relation to the saidwinding, and an inner lining of magnetic metal, substantially asdescribed.

3. In an electric meter,the combination with an armature-Winding, of anouter shell of nonmagnetic metal fixed with relation to the saidwinding, and an inner body of magnetic metal also fixed with relation tothe said winding, substantially as described.

In testimony that I claim the foregoing as my invention I affix mysignature, in presence of two subscribing witnesses, this 17th day ofApril, A. D. 1899.

THOMAS DUNCAN.

\Vitnesses:

HENRY WV. CARTER, ALBERT H. GRAVES;

